IETester is easy to use. You first select the version of IE to be used for testing:
Notice that you can choose to test pages with IE5.5, IE6, IE7, or IE8, and there is an option to test a page in all IE versions where each version is displayed in a separate tab.
The next step is to enter the URL of the page to be tested:
In the above example, the option to test in all IE versions was selected. Once you enter the URL and click OK, the page is displayed in separate tabs:
IETester is still in Alpha release and it has some bugs, but I have been able to use it to test sites and it has alerted me to some problems. You can learn more about IETester and download a free copy from http://www.my-debugbar.com/wiki/IETester/HomePage.